The present invention relates to magnetizing an element to serve as a permanent magnet in a magnetic system and circuit.
Permanent magnets are frequently provided as such in that the element to be magnetized is installed in the system in which it is to be used, and thereafter a strong magnetizing field is applied. Following cessation of the application of that field, the system settles to a particular magnetic state in which the now completed permanent magnet experiences particular load conditions. Particularly, the magnet will have a particular magnetic induction at a particular magnetic field establishing an operating and working point. This point in the induction field diagram is determined essentially by two conditions. One condition is established by the magnetic conduction of the entire magnetic system, e.g. the minimum magnetic flux values loading the magnet. The other condition is the quality of the magnetic material expressed quantitatively as the demagnetization curve of the magnet.
In order to arrive at a particular operating point, care must be taken that the magnetic conduction of the magnetic system (including conduction through stray fields) is accurately arrived at through production of exact geometric dimensions and through accurately predetermined magnetic characteristics of the components participating in the system. Moreover, the particular permanent magnetic material must have an accurately determined demagnetization curve. With regard to each individual system this can readily be provided for. However, the situation is different if many similar systems are to be made, e.g. polarized electromagnetic relays, each to have the same effective properties such as response, holding force, etc. Particularly, the demagnetization curve must be expected to differ from magnet to magnet, possibly even to a considerable extent. Thus, otherwise seemingly similar systems, when magnetized under similar conditions, must be expected to settle at different operating points. Deviations in magnetic permeance of one or the other of the circuit components add (possibly) to the deviation resulting from differing demagnetization curves. This means that, for example, such relays do have different response times, different contact forces, different forces of magnetic attraction, etc. Generally speaking, the different magnetic systems may operate quite differently simply because the permanent magnetic bias differ.
Aside from the foregoing, it must also be considered that externally applied electromagnetization introduced in the system may demagnetize partially the permanent magnet therein, so that its operating point is shifted. This can readily occur, for example, in a polarized relay when the energizing current is too strong for any reason. The relay may loose its polarity more or less, or the magnet may even reverse its magnetization. In either case, the relay is no longer usable.
Previously, one has tried to adjust the actual operating point of such a magnetic system by changing the magnetic conduction of one or another of its components. In connection therewith it has been suggested to include weak magnetic shunt paths in parallel to the permanent magnet, and these shunts were then varied as was deemed necessary. Modifications in these shunts do permit compensation of variations in the conduction elsewhere in the system and from system to system. Also, the demagnetization curves could be modified to some extent so that minor errors in the resulting working and operating point could be corrected. However, such adjustment is rather time-consuming and highly individual for each system and its magnet or magnets.